1. Field of the Invention:
The present invention relates to an excimer laser apparatus having a circulating fan for producing a high-speed laser gas stream, and more particularly to an excimer laser apparatus having a feature in a motor for rotating a shaft of a circulating fan and a magnetic bearing for supporting the shaft of the circulating fan.
2. Description of the Related Art
FIG. 5 is a schematic view showing a structure of a conventional excimer laser apparatus. As shown in FIG. 5, the conventional excimer laser apparatus comprises a container 41 sealing a laser gas including a halogen gas such as a fluorine gas therein, ionization electrodes (not shown) disposed in the container 41 for ionizing the laser gas, and discharge electrodes 42, 42 disposed in the container 41 for inducing an electric discharge capable of oscillating a laser light. A circulating fan 43 for producing a high-speed laser gas stream between a pair of the discharge electrodes 42 and 42 is disposed in the container 41.
The circulating fan 43 has a shaft 44 penetrating therethrough and protruding from both ends thereof. The shaft 44 is supported in a non-contact manner by radial magnetic bearings 51, 52 provided at both ends of the container 41, and by an axial magnetic bearing 53 provided at one end of the container 41. A motor 54 is provided at a shaft end side of the radial magnetic bearing 52.
Displacement sensor targets 51c, 51c and electromagnet targets 53d, 52d of the radial magnetic bearings 51, 52, and a displacement sensor target 53d and an electromagnet target 53e of the axial magnetic bearing 53 are secured to the shaft 44. Further, a rotor 54b of the motor 54 is secured the shaft 44. Displacement sensors 51a, 52a, 53a , electromagnets 51b, 52b, 53b, 53c, and a stator 54a of the motor 54 are disposed at positions opposed to the displacement sensor targets 51c, 52c , 53d , the electromagnet targets 51d, 52d, 53e, and the rotor 54b. 
Thin cylindrical bulkheads 55, 56 are provided on inner peripheral surfaces of the displacement sensors 51a, 52a and the electromagnets 51b, 52b of the radial magnetic bearings 51, 52, and the stator 54a of the motor 54. The bulkheads 55, 56 are formed of a material having corrosion resistance to the halogen gas included in the laser gas, e.g., austenitic stainless steel such as SUS316L. The bulkheads 55, 56 prevent the displacement sensors 51a, 52a, the electromagnets 51b, 52b, and the stator 54a from contacting the laser gas.
Like the radial magnetic bearings 51, 52, a bulkhead 57 is provided on the inner peripheral surface of the displacement sensor 53a of the axial magnetic bearing 53 to prevent the displacement sensor 53a from contacting the laser gas. The electromagnets 53b, 53c comprise cores formed of a ferromagnetic material having corrosion resistance to the halogen gas included in the laser gas, e.g., permalloy, and have bulkheads 58 provided only on the coils thereof.
The displacement sensor targets 51c, 52c , 53d and the electromagnet targets 51d, 52d, 53e of the radial magnetic bearings 51, 52 and the axial magnetic bearing 53 secured to the shaft 44 are disposed in airtight spaces communicating with the container 41. Therefore, the displacement sensor targets 51c, 52c , 53d and the electromagnet targets 53d, 52d, 53e are formed of a ferromagnetic material having corrosion resistance to the halogen gas, e.g., permalloy. The rotor 54b of the motor 54 is composed of a composite of a silicon steel plate and an aluminum alloy, and a permanent magnet. Therefore, a thin cylindrical bulkhead 59 is provided on the outer peripheral surface of the rotor 54b. The bulkhead 59 forms a sealed structure to prevent the rotor 54b from contacting the laser gas.
As described above, the conventional excimer laser apparatus requires the displacement sensors 51a, 52a, 53a and the electromagnets 51b, 52b, 53b, 53c of the radial magnetic bearings 51, 52 and the axial magnetic bearing 53, which are sequentially arranged in the axial direction. Therefore, the axial length of the shaft 44 is long, and the critical speed of the shaft 44 is decreased. Particularly, high-power laser light with continuous oscillation has been demanded in recent excimer laser apparatus. In order to perform continuous oscillation, it is necessary to replace the laser gas between the discharge electrodes 42 and 42 in a shorter time. Thus, it is necessary that the speed of the laser gas stream produced by the circulating fan 43 should be increased. Accordingly, the circulating fan 43 needs to be rotated at a high speed. However, when the axial length of the shaft 44 increases, the critical rotational speed decreases, so that it is difficult to rotate the circulating fan 43 at a high speed.
If the power of the motor 54 is increased to rotate the circulating fan 43 at a high speed, the motor 54 increases in rotational driving force and also increases in magnetic attraction force in the radial direction. This radial magnetic attraction force causes vibrations to the shaft 44. In order to cancel out the vibrations, the electromagnets 51b, 52b of the radial magnetic bearings 51, 52 need to be increased in magnetic force. Consequently, it is necessary to simultaneously achieve the increase in the power of the motor 54, and the enhancement of the magnetic force of the electromagnets 51b, 52b of the radial magnetic bearings 51, 52. This causes both of the radial magnetic bearings 51, 52 and the motor 54, and their installation spaces to be larger.
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide an excimer laser apparatus which can solve the above drawbacks with a conventional excimer laser apparatus, and can facilitate high-speed rotation of a circulating fan, and requires reduced installation spaces for a bearing portion and a motor portion.
According to an aspect of the present invention, there is provided an excimer laser apparatus having a container sealing a laser gas including a halogen gas therein, a pair of discharge electrodes disposed in the container for inducing an electric discharge capable of oscillating a laser light, and a circulating fan with a shaft for producing a high-speed laser gas stream between a pair of the discharge electrodes, the excimer laser apparatus characterized in that: both ends of the shaft are rotatably supported by rotor-stator mechanisms, or one end of the shaft is rotatably supported by a rotor-stator mechanism, and the other end of the shaft is supported by a magnetic bearing; and the rotor-stator mechanism comprises a rotor formed of a magnetic material and attached to the shaft of the circulating fan, a stator provided at a position opposed to the rotor, an electric motor winding provided in the stator for applying torque to the rotor, and a position control winding provided in the stator for producing a magnetic force to levitate and support the rotor.
As described above, the rotor-stator mechanism comprises the rotor formed of a magnetic material and attached to the shaft of the circulating fan, the stator provided at a position opposed to the rotor, the electric motor winding provided in the stator for applying torque to the rotor, and the position control winding provided in the stator for producing a magnetic force to levitate and support the rotor. The end of the shaft is rotatably supported by the rotor-stator mechanism. This arrangement can eliminate the need to provide cores for electromagnets of the magnetic bearing and the motor. Therefore, the shaft length of the shaft can be shortened, and the installation spaces for the magnetic bearing and the motor can be reduced. Accordingly, since the critical speed of the shaft can be increased, the circulating fan can be easily rotated at a high speed. Further, the excimer laser apparatus can be downsized.
Further, a magnetic attraction force in the radial direction produced by the electric motor winding of the rotor-stator mechanism can be controlled so as to be cancelled out by a magnetic force produced by the position control winding, for thereby eliminating vibrations to be caused to the shaft.
In a preferred aspect of the present invention, a bulkhead is provided on an inner peripheral surface of the stator in the rotor-stator mechanism to locate the stator outside of the container for preventing the stator from contacting the laser gas.
As described above, the bulkhead is provided on the inner peripheral surface of the stator in the rotor-stator mechanism. Thus, the bulkhead can prevent the stator core, the electric motor winding, the position control winding, and the like constituting the stator with low corrosion resistance from contacting the laser gas including the halogen gas. Therefore, these members can be protected from corrosion. Furthermore, since the stator is not corroded by the laser gas, the laser gas is not contaminated with particles generated by corrosion. Thus, stable operation for a long term can be achieved.
In a preferred aspect of the present invention, a bulkhead is provided on an outer peripheral surface of the rotor in the rotor-stator mechanism to prevent the rotor from contacting the laser gas.
As described above, the bulkhead is provided on the outer peripheral surface of the rotor in the rotor-stator mechanism. Thus, the bulkhead can prevent the rotor from contacting the laser gas. Therefore, the rotor can be formed of a ferromagnetic material, a permanent magnet, or the like, regardless of corrosion resistance to the laser gas. Accordingly, a rotating machine with high efficiency can be obtained. Furthermore, since the rotor is not corroded by the laser gas, the laser gas is not contaminated with particles generated by corrosion. Thus, stable operation for a long term can be achieved.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.